linux-kernel - Re: [RFC PATCH] x86: Move away from /dev/cpu/*/msr

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Date:	Wed, 15 Jun 2016 16:00:28 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	chenyu <yu.chen.surf@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Thomas Renninger <trenn@...e.com>,
	Kan Liang <kan.liang@...el.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] x86: Move away from /dev/cpu/*/msr

On Wed, Jun 15, 2016 at 12:36:22PM +0200, Borislav Petkov wrote:
> Ah, yes, good point. Will change.

Ok, got a bit more involved - I also need to disable preemption around
smp_call_function_single(). Here's what I have now. It seems to work
too.

static ssize_t
energy_policy_pref_hint_show(struct device *dev, struct device_attribute *attr,
                             char *buf)
{
        u64 epb;

        preempt_disable();
        if (rdmsrl_on_cpu(dev->id, MSR_IA32_ENERGY_PERF_BIAS, &epb))
                epb = -1;
        preempt_enable();

        return sprintf(buf, "%d\n", (unsigned int)(epb & 0xFULL));
}

static ssize_t
energy_policy_pref_hint_store(struct device *dev, struct device_attribute *attr,
                              const char *buf, size_t count)
{
        u32 val;
        u64 epb;

        if (kstrtou32(buf, 10, &val) < 0)
                return -EINVAL;

        if (val > 15)
                return -EINVAL;

        preempt_disable();

        if (rdmsrl_on_cpu(dev->id, MSR_IA32_ENERGY_PERF_BIAS, &epb)) {
                count = -EINVAL;
                goto out;
        }

        if ((epb & 0xf) == val)
                goto out;

        if (wrmsrl_on_cpu(dev->id, MSR_IA32_ENERGY_PERF_BIAS, (epb & ~0xFULL) | val))
                count = -EINVAL;

out:
        preempt_enable();
        return count;
}

-- 
Regards/Gruss,
    Boris.

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